Traffic detecting apparatus



Dec. 27, 1 4 MARTIN 2,492,388

TRAFF IC DETECTING APPARATUS Filed Nov. 2'7, 1945 IN VEN TOR azmMaptm.

HS A TTORNE Y Patented Dec. 27, 1949 TRAFFIC DETECTING APPARATUS Paul N. Martin, Penn Township, Allegheny Conn ty, Pa, assignor to The Union Switch & S1gnal Company, Swissvale, Pa., a corporation of Pennsylvania Application November 27, 1945, Serial No. 631,159.

8 Claims. 1

My invention relates to traffic detecting apparatus, and more particularly, to electronic means for detecting presence of a vehicle in an extended stretch of roadway which does not depend upon physical contact with circuit controlling elements in the roadway, such as highway contactor or railway track circuits.

The principal object of my invention is the provision of improved vehicle detecting means in which the presence of a vehicle at any point in an extended stretch of roadway is detected by its efiect upon an alternating electric field of force in the space above the roadway occupied by the vehicle. My invention is particularly applicable to railway vehicles, and may be applied to a railway to supplement or as a substitute for, a track circuit, as for example, to detect the presence of a car in a stretch of track of which the rails have a high contact resistance due to infrequent train movements, or to detect the presence of light weight vehicles, or of highway vehicles or the like having insulated wheels and incapable of shunting the usual track circuits, or to detect the presence of cars on railway crossings or at other locations where the installation of track circuits is impracticable.

I shall describe one form of apparatus embodying my invention and shall then point out the novel features thereof in claims.

In the accompanying drawing, Fig. 1 shows one form of train-detecting apparatus comprising an electronic oscillator, the circuits for which are so arranged that it is responsive to changes in the electrical capacity to ground of insulated conductors I and 2, which extend along a stretch of roadway 3, such as a single track highway or a railway along which vehicles may move, but which restrains them to remain at a substantially constant distance from conductors I and 2, the apparatus serving to detect the presence of a vehicle at any point in the stretch by the release of a detector relay R. which is normally held energized by current generated by the oscillator. Figs. 2a, 2b and 2c illustrate different Ways in which the conductors I and 2 may be disposed to render the apparatus more sensitive to the presence of a train. The roadway 3 is illustrated in Fig. 2a as a single track highway occupied by a highway vehicle 4a, and in Figs. 2b and 20, as a pair of track rails 3a and 31) for guiding the wheels of a railway car or train 4?). Fig. 3 shows-a specific application of the apparatus of my invention to the problem of detecting the presence of a railway car or train on the tracks of a railway crossover.

Similar reference characters refer to similar parts in each of the views, and in lieu of showing the various sources ofcurrent for energizing the apparatus, I have shown only their termi-. nals, the positive or supply terminal being identified by the reference character B and the negative or common return terminal by the reference character C, in each instance.

Referring to Fig. 1, the electron tube VI has its plate to cathode circuit energized over connections from the plate of the tube to terminal B of the local source through a choke coil L4, and from the cathode of the tube to terminal C of the source through an inductance L2. The inductances LI and L2, in series, are tuned by a capacity CI toform a tank circuit having one end terminal connected to the plate of tube VI through a blockingv condenser C4, and the other end terminal through conductor 2, an adjustable condenser C2 and conductor I, to the grid of. tube VI, whereby a voltage derived from the tube output may be impressed across the gridcathode circuit of the tube of the proper value and phase to cause. the generation of sustained oscillations of a frequency determined by. the circuit constants. Coupled to the-inductances LI and L2 is a tuned inductance or filter L3 by which voltage of the frequency normally gen-. erated by tube VI is supplied to the grid circuit of an amplifier tube V2,: the. output of which is supplied through va filter L5- selectively responsive to the same frequency, to energize a direct current relay R connected thereto through a rectifier whereby relay R- is normally held energized. .v

The conductors I and 2 which extend along the roadway 3 where the detection of the presence of a vehicle is desired may be arranged as shown in Fig. 2a, 2b or 20, or'othe'rwise, conductor 2 being interposed in the direct path between 0011- ductor I and the grounded roadway in Fig. 2a or between conductor I and the track rails in Figs. 2b and 2c. The arrangement of Fig. 2a may also be applied to detect the intrusion of an object suchas a vehicle intoan enclosure such as a bridge or a room in which the structure corresponding to the ground 3 completely surrounds the vehicle and the conductors I and 2 and is not directly associated with the earth. Although for simplicity, the conductors are represented as wires they may also consist of metallic plates or screens, or a plurality of wires connected in parallel as inthough the'car fails to shunt the track relay TRI or TRZ, due to the high contact resistance of the rails 3. Relay NWP is arranged as a stick relay. and the detecting apparatus D is normally de energized. When the switches WI and W2 are restored to normal. and locked by the train crew, the detecting apparatus is supplied with. current over a connection tot-erminal 13 including back contact a of relay NW? and the switch circuit controller contacts N, tube VI is set into oscillation to create an oscillating electric field in the space above the crossover track, and then the detector relay R becomes energized, provided there are no cars within range of the detector wires 1 and 2. Relay R completes a pick-up circuit for relay NWP which then becomes energized, and by opening its back contact a, deenergizes the detector apparatus and releases relay R.

Although I have herein shown and described only one form of apparatus embodying my invention, it is understood that various changes and modifications may be made therein within the scope of the appended claims without departing from the spirit and scope of my invention.

- Having thus described my invention, what I claim is:

1. Traffic detecting apparatus for indicating the presence of a vehicle in a stretch of track, comprising an electron tube having a plate, grid and cathode; a tank circuit including inductance and capacity having one end terminal connected directly to ground and through a blocking condenser to said plate, a middle terminal connected to said cathode, and its other end terminal ungrounded and capacity coupled to said grid, whereby said tube is conditioned to generate sustained oscillations of a frequency determined by the constants of said tank circuit, an insulated conductor included in the connection of said ungrounded end terminal to the grid of said tube, said conductor extending the length of said stretch of track and having a capacity to ground which is normally low in comparison with the coupling capacity between the grid and said ungrounded tank circuit terminal but which capacity is increased by the presence of a vehicle in said stretch of track sufliciently to reduce the voltage supplied to the grid to less than that required to sustain oscillations, and a detector relay energized by the oscillations generated by said tube when said stretch of track is unoccupied.

2. Trafiic detecting apparatus comprising, an insulated conductor extending the length of a stretch of substantially grounded trackway, an electronic oscillator comprising an electron tube having a plate, grid and cathode, and a tank circuit having one end terminal grounded and connected through a condenser to said plate, a middle terminal connected to said cathode, and the other end terminal connected by said conductor through a second condenser to said grid, the capacity of said second condenser being sufficient relative to the capacity in the space between said conductor and trackway of the electric field between said conductor and ground, to render the tube effective to generate oscillations when said space is wholly unoccupied but not when there is a vehicle in said stretch, a detector relay, and means for maintaining said detector relay energized by the oscillations which are generated by said tube when said stretch is unoccupied.

3. Traflic detecting apparatus comprising, two conductors which extend the length of a stretch of substantially grounded trackway, the relative positions of said conductors being sues that the first conductor normally has a relatively low capacity to ground due to the shielding effect of the second but has a relatively high capacity to ground when the stretch is occupied by a vehicle, a voltage divider including an adjustable condenser and the capacity to ground of said first conductor in series, connected between said second conductor and ground, an electronic oscillator having a grid circuit and a plate circuit, a detector relay normally energized by current supplied by said plate circuit, means including said plate circuit for normally maintaining a potential difference between said second conductor and ground, and means including said voltage divider for supplying a voltage to the grid circuit of said oscillator which is sufiicient to maintain oscillations only when the stretch is not occupied by a vehicle. i

4. Trafiic detecting apparatus comprising, two

insulated wayside conductors which extend the length of a stretch of substantially grounded roadway, so located that the first conductor normally has a relatively low capacity to ground due to the shielding efiect of the second conductor,

but has a relatively high capacity to ground when the stretch is occupied by a vehicle, an electronic oscillator having its output controlled by a tank circuit comprising an inductance and a capacity which includes that of the space between the second conductor and ground and having its input circuit connected to said first conductor, a detector relay normally energized by current derived from the output of said oscillator, and means including a condenser connected between said two conductors for so adjusting the voltage supplied to said oscillator from said first conductor as to effect the release of said detector relay when a vehicle occupies said stretch.

5. Traffic detecting apparatus comprising, two insulated wayside conductors which extend the length of a stretch of substantially grounded roadway and are connected by an adjustable condenser said conductors being so located that the first normally has a relatively low capacity to ground due to the shielding effect of the second but has a relatively high capacity to ground when the stretch is occupied by a car, an electronic oscillator having its output circuit controlled by a tank circuit connected between said second conductor and ground and having its input circuit connected to said tank circuit over said two conductors and said adjustable condenser in series, a detector relay normally energized by current derived from the output circuit of said oscillator, and means including said adjustable condenser for supplying a voltage to said input circuit sufiicient to maintain oscillations only when the stretch is not occupied by a vehicle.

6. Traffic detecting apparatus comprising, two insulated wayside conductors which extend the length of a stretch of substantially grounded trackway, the first of which is at a greater efiective distance from the trackway than the second, an electronic oscillator for supplying alternating current to said second conductor to maintain a potential difference between such conductor and the trackway, said oscillator deriving its energization from a potential divider comprising a capacity connection through space from said first conductor to the trackway and a connection through an adjustable condenser to said second conductor, and means comprising a vehicle in said stretch for decreasing the effective distance areas-es 7. A system for detecting the intrusion of a' movableobject in a protected space, comprising a first and. a secondconductor adjoining said space, a source of electrical energy, means for supplying a voltage from said source to said first conductor to create an electric field of force between said first conductor andground, means for supplying a yoltage from said source to said second conductor, .said conductors being so positioned relative to ground and to said space that the potential impressed on. the second conductor directs said electric field. away from its normal path into said space, and a detector responsive to an increase in the strength of said electric field due to the movement-10f an object-of a predetermined size into said space.

.8. A system for detecting the intrusion of a 20 movable object in a protected space, comprising a first and a second conductor adjoining said space, a source of electrical energy, means for supplying a voltage from said source to said first conductor to create an electric field of force between said first conductor. and ground, means for supplying a relatively higher voltage from said source to said second conductor, said second conductor being so located between the first con doctor and ground that the potential impressed thereon directs said electric field away from its normal path to ground and concentrates said field in said space, and a detector responsive to an increase in the strength of said electric field due to the movement of an object of a predetermined size into said space.

PAUL N. MARTIN.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS OTHER REFERENCES 25 An article entitled Electronic Protective Systems, by Maxwell H. Lindsay, on pages 367-374 of Electrical Engineering, of October 1944. (Copy in Div. 42.) 

